Waiting for 9.5 – Add transforms feature

Add transforms feature
This provides a mechanism for specifying conversions between SQL data
types and procedural languages. As examples, there are transforms
for hstore and ltree for PL/Perl and PL/Python.
reviews by Pavel Stěhule and Andres Freund

After this was committed, there were subsequent patches that modified how it works, but the general idea is that we now have transforms, that work.